The invention concerns a below-floor lathe for reprofiling the rims of railroad-vehicle wheel-sets, with four driven friction rollers, two turning tool supports, and controls, whereby the friction rollers can be forced in pairs against the outer surface of each wheel rim in a wheel set.
A below-floor lathe of the aforesaid type is known from the July 1987 version of Hoesch Maschinenfabrik Deutschland AG Brochure 222.
The driven friction rollers in a lathe of this type establish the rotation and cutting motion of the wheel set.
The frictional forces transferred to the wheel set by the friction rollers are relatively small because, first, the supporting force of the friction rollers must not exceed the maximum axial load on the wheel set and, second, the coefficient of friction between the friction rollers and the surface of the rims is low. The coefficient of friction is especially detrimentally affected when dirt and/or grease adheres to the surface of the rims.
Since the coefficient of friction fluctuates widely, the friction rollers will sometimes slide over the surface of the rims while a wheel set is being machined in the known lathe. The drawback is that it takes longer to machine the wheel set.